Do not remove texinfo outputs upon mostlyclean.

Do not remove texinfo outputs upon mostlyclean.

* lib/am/texinfos.am: New substitutions %MOSTLYCLEAN%,
%MAINTCLEAN%.
(clean-aminfo): New target, remove %TEXICLEAN% if nonemtpy,
declare phony.  Hook this target to ...
(clean-am): ... this and ...
(?CYGNUS?clean-info): ... this.
(maintainer-clean-aminfo): Remove %MAINTCLEAN% if nonempty,
for later.
(mostlyclean-aminfo): Remove %MOSTLYCLEAN%.
* automake.in (handle_texinfo_helper): Return three arrays
$MOSTLYCLEAN, $TEXICLEAN, $MAINTCLEAN, instead of one array.
Only put LaTeX helper files in $MOSTLYCLEAN, the rest in
$TEXICLEAN for now.
(handle_texinfo): Accept these, chop off extra newline, and
substitute them in `texinfos.am'.
* NEWS: Update.
* tests/txinfo33.test: New test.
* tests/Makefile.am: Update.
Report by Bruno Haible.

Signed-off-by: Ralf Wildenhues <Ralf.Wildenhues@gmx.de>